Optic fibre is used in oil and gas wells to transmit light waves carrying signals to surface. Hydrogen is invariably present in the hydrocarbon environment of oil and gas wells. At temperatures above 170 degrees Celsius, optic fibre is susceptible to attack from hydrogen atoms. The hydrogen atoms penetrate protective coverings and react with the optic fibre. This results in a degradation of the signals due to scattering of the light waves. This signal degradation has come to be known as “hydrogen darkening”. Canadian Patent 2,323,042 discloses a method of reducing the time until hydrogen darkening occurs by placing the optic fibre within a tube containing a protective liquid.